Jeremy Ngakia has joined Watford on a free transfer after leaving West Ham on July 1.
The 19-year-old left West Ham last month following the expiration of his contract, having failed to agree terms on a new deal.
Ngakia, who also attracted interest from Bundesliga side Schalke, becomes Watford's first signing since their relegation from the Premier League.
He will join up with the Watford squad for pre-season training next week as the prepare for their first season in the Championship since 2015.
Watford remain without a permanent manager but Serbian Vladimir Ivic has emerged as the front-runner to succeed Nigel Pearson.
Ngakia broke into the West Ham team prior to the shutdown due to the coronavirus pandemic and impressed in two matches against eventual champions Liverpool.
Though he wanted an improvement on the scholarship deal he was receiving at West Ham, Ngakia was keen to base any decision on his next move on playing time rather than an increased wage.
Ngakia was not given assurances by West Ham that he would be a first-team regular, with Ryan Fredericks and Ben Johnson already at the club.
As a result, the young defender has been convinced to join Watford due to the increased chance of gaining consistent experience as a first-team player.
West Ham are also exploring the possibility of adding a new right-back to their squad this summer as David Moyes aims to put his own stamp on the club.
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The summer transfer window will run for 10 weeks from July 27 and close at 11pm on October 5.
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