Given this text, who was Mclaren's number-one driver in 1988

In 1988, due to the relationship he had built up with Honda throughout the 1987 season with Lotus, and with the approval of McLaren's number-one driver and then-double world champion, Alain Prost, Senna joined the McLaren team.[54] The foundation for a fierce competition between Senna and Prost was laid, culminating in a number of dramatic race incidents between the two over the next five years.[55] However, the experienced pair also quickly realized, despite their personal rivalry, they had to work together, especially in testing, to keep ahead of their main opposition from Ferrari, Williams, Benetton and Lotus.

In 1988, according to this text Alain Prost was McLaren's number one driver