Like Foxes team-mate Wilfred Ndidi, Castagne’s professional career began at Jupiler Pro League side K.R.C. Genk, following his debut in Limburg with another 27 appearances for the club as Blauw-Wit narrowly missed out on UEFA Europa League qualification in 2014/15.
Despite his tender age, Arlon-born Castagne was quickly transformed from talented youngster into first-team star, adding another 40 outings in his final year at Cristal Arena.
His high level of performances, typified by both scoring goals for his club and denying others at the opposite end of the pitch, led eventually to a switch to Atalanta in 2017.
Gian Piero Gasperini saw Castagne as a vital ingredient in his plans to build a vibrant, ambitious Atalanta outfit who would go on to regularly upset the established order in Italy.
In four seasons – three of which involving Castagne - I Nerazzurri banished memories of regular battles to avoid relegation and replaced them with aspirations to challenge in Europe.
His quality on the flanks has been a real tool for Gasperini and Atalanta, leading to successive third-placed finishes in Serie A and culminating in a run to the Champions League Quarter-Finals earlier in 2020, beating Dinamo Zagreb, Shakhtar Donetsk, and Valencia along the way.
Castagne stands alongside the likes of Josip Iličić and Luis Muriel in being an embodiment of Atalanta’s rapid rise – earning him a maiden Belgium call-up in September 2018.
Since then, he's scored for his country twice – against Kazakhstan and San Marino – while also being a creative spark for Roberto Martínez's side, who sit top of the FIFA World Rankings.
Although nobody knew it at the time, a potential glimpse into the future came on 22 March, 2019 when Castagne laid it up for Youri Tielemans to slot home Belgium’s first in a 3-1 win in Russia.
Able to play on either side of a back-four, or in a more advanced wing-back position, the talented full-back has now made seven international appearances and is integral to Martínez's plans.
Over the years, Castagne has been linked with some of the biggest clubs in Europe and played a part in Leicester City’s fifth campaign in continental football across 2020/21 - reaching the Round of 32 in the UEFA Europa League.
The crowning moment of his first year in Leicester, however, was undoubtedly his sterling performance in a 1-0 win over Chelsea at Wembley Stadium in May 2021 as the Foxes ended their 137-year wait to lift the Emirates FA Cup.
Although curtailed by injury in 2021/22, Castagne remains a key figure for Leicester, helping the Club reach the semi-finals of the UEFA Europa Conference League and scoring a magnificent goal against Brentford in March 2022.