  We present the pulsar timing analysis of the accreting millisecond X-ray
pulsar SWIFT J1749.4-2807 monitored by NICER and XMM-Newton during its latest
outburst after almost eleven years of quiescence. From the coherent timing
analysis of the pulse profiles, we updated the orbital ephemerides of the
system. Large phase jumps of the fundamental frequency phase of the signal are
visible during the outburst, consistent with what was observed during the
previous outburst. Moreover, we report on the marginally significant evidence
for non-zero eccentricity ($e\simeq 4\times 10^{-5}$) obtained independently
from the analysis of both the 2021 and 2010 outbursts and we discuss possible
compatible scenarios. Long-term orbital evolution of SWIFT J1749.4-2807
suggests a fast expansion of both the NS projected semi-major axis $(x)$, and
the orbital period $(P_{\rm orb})$, at a rate of $\dot{x}\simeq 2.6\times
10^{-13}\,\text{lt-s}\,\text{s}^{-1}$ and $\dot{P}_{\rm orb}\simeq 4 \times
10^{-10}\,\text{s}\,\text{s}^{-1}$, respectively. SWIFT J1749.4-2807 is the
only accreting millisecond X-ray pulsar, so far, from which the orbital period
derivative has been directly measured from appreciable changes on the observed
orbital period. Finally, no significant secular deceleration of the spin
frequency of the compact object is detected, which allowed us to set a
constraint on the magnetic field strength at the polar caps of
$B_{PC}<1.3\times 10^{8}~\text{G}$, in line with typical values reported for
AMXPs.
